Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
  • B32B7/04—Interconnection of layers
  • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B21/00—Layered products comprising a layer of wood, e.g. wood board, veneer, wood particle board
  • B32B21/04—Layered products comprising a layer of wood, e.g. wood board, veneer, wood particle board comprising wood as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B21/06—Layered products comprising a layer of wood, e.g. wood board, veneer, wood particle board comprising wood as the main or only constituent of a layer, which is next to another layer of the same or of a different material of paper or cardboard
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B23/00—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose
  • B32B23/04—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose comprising such cellulosic plastic substance as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B23/06—Layered products comprising a layer of cellulosic plastic substances, i.e. substances obtained by chemical modification of cellulose, e.g. cellulose ethers, cellulose esters, viscose comprising such cellulosic plastic substance as the main or only constituent of a layer, which is next to another layer of the same or of a different material of paper or cardboard

Definitions

• the present invention relates to flexible polymeric film packaging structures with improved oxygen, flavor/odor, grease/oil and moisture barrier characteristics. More specifically, the invention relates to a film structure which includes a polymeric substrate, an oxygen barrier containing cross-linked polyvinyl alcohol (“PVOH”) and a moisture barrier selected from cellulose material, polyvinylidene ( • ⁇ PVdC”) coating and metallized polymeric composite.
• PVOH cross-linked polyvinyl alcohol
• Certain polymeric films employed for the packaging of foods inherently permit the transmission of oxygen and moisture from the outside of the film to the inside of a food package wrapped with the film.
• Oxygen and/or moisture permit rapid deterioration of foods packaged in polymeric films. Exclusion of oxygen and moisture from packaged foods retards product spoilage.
• film structures which provide a barrier to oxygen, flavor/odor, grease/oil and moisture are highly desirable food packaging materials.
• PVOH Polyvinyl alcohols are polymers containing (-CH 2 - CHOH-) groups. They can be applied from water solution and are in many respects attractive materials for use as barrier coatings for thermoplastic polymer .substrates.
• polyvinyl alcohols When applied to thermoplastic polymer surfaces which have been treated by any of a number of means to render them receptive to coatings, polyvinyl alcohols adhere adequately, are flexible, clear and transparent, provide an oxygen impermeable barrier, and are resistant to permeation by greases, oils and a wide variety of common organic solvents, such as esters, ethers, ketones, hydrocarbons and chlorinated hydrocarbons.
• the present invention which addresses the needs of the prior art, provides packaging film structures which have low oxygen, flavor/odor, grease/oil trans issive charactristics and high moisture barrier properties. More specifically, it has now been found that by securing a film combination which has low oxygen transmissive properties to a moisture barrier including (1) cellulose material, preferably box board; (2) polyvinylidene chloride coating; or (3) metallized polymeric composite, preferably metallized polypropylene, film structures having enhanced oxygen, flavor/odor, grease/oil transmissive characteristics, and high moisture barrier are obtained.
• the film structure of this invention includes a polymeric substrate adapted to receive an oxygen barrier layer by surface treating and priming of at least one side thereof.
• the surface of the polymeric substrate is provided with an oxygen barrier layer which includes PVOH cross-linked with a cross-linking agent in the presence of a catalytic amount of inorganic acid, preferably sulfuric acid.
• a cellulose material is to be the moisture barrier of the film, it is then laminated by adhesion onto the outer surface of the oxygen barrier of the film structure.
• the adhesive is preferably polyurethane or polyethylene.
• the cellulose material is preferably paperboard or fiberboard, and most preferably box board.
• the film structure polymeric core has both surfaces treated to receive other coatings.
• the surface treatment is accomplished by well known methods in the art, corona or flame treatment being preferred. Both surfaces of the polymeric core may then be primed. Poly(etyleneimine) is used for the PVOH receiving surface, and epoxy is used for the PVdC receiving surface.
• the polymeric core is provided on one surface with a cross-linked PVOH layer, as above, and on the other surface, the polymeric core is coated with PVdC.
• a metallized polymeric film is laminated by adhesion or extrusion onto the outer surface of the oxygen barrier of the film structure.
• the adhesive is preferably polyurethane or polyethylene for extrusion lamination.
• the metallized polymeric film is preferably metallized oriented polypropylene.
• the polymeric substrate may be oriented polyethylene terephthalate, nylon, polypropylene and polyethylene.
• the core may also include a coextruded propylene-ethylene copolymer skin.
• the polymeric substrate is usually surface treated by known processes, preferably corona treatment, to a surface free energy of 35 dynes/cm or higher.
• the present invention also provides a process for preparing packaging film structures having improved oxygen and moisture barrier properties.
• the process includes coating at least one surface of a primed, surface treated polymeric substrate with an aqueous solution of PVOH, aldehyde-containing crosslinking agent and a catalytic amount of inorganic acid, preferably sulfuric acid, and allowing the polyvinyl alcohol to cross-link thus forming an oxygen barrier.
• the aqueous solution of PVOH includes a solid content comprising from 62.5% to 95% by weight of PVOH, from 5% to 30% by weight of crosslinking agent and up to 7.5% by weight of acid catalyst. If a cellulose material is to be the moisture barrier of the film, it is then secured to an outer surface of the oxygen barrier by adhesion lamination.
• packaging film structures made by the above process are also encompassed by the present invention.
• packaging film structures are provided which have excellent oxygen, flavor/odor, grease/oil, and moisture barrier properties.
• the film structures of the present invention having a moisture barrier comprising a cellulose material have been found to be especially useful in a packaging of tomato sauces, condiments, wines, juices and detergents, in which it is important that the flavor or odor of the foodstuffs is contained within the package.
• the layer of cross-linked PVOH coating used in the present invention may be used at thinner gauges than other oxygen barrier layers. For example, less than 0.05 mils of cross-linked PVOH provides an oxygen barrier which is as effective as 0.48 mils of EVOH coating.
• the film structure having a moisture barrier comprising a PVdC coating is also transparent and heat sealable.
• the film structure consists of at least two coextruded mono webs.
• Fig. 1 shows a cross-sectional view of one embodiment of the present invention, wherein the foodstuff is next to the sealant coated cellulose material.
• Fig. 2 shows a cross-sectional view of another embodiment of the present invention, wherein the foodstuff is next to the sealant coated polymeric substrate.
• Fig. 3 illustrates one embodiment of the present invention, wherein primer coatings have been applied to both surfaces of the polymeric core.
• Fig. 4 shows a cross-sectional view of another embodiment of the present invention.
• Certain barrier film combinations have excellent oxygen barrier properties. However, for certain commercial applications the moisture barrier properties of these films can be improved.
• the present invention provides a (1) cellulose bearing, (2) PVdC coated, or (3) metallized polymeric film structure including oxygen, flavor/odor, grease/oil, and moisture barriers.
• the oxygen barrier includes cross-linked PVOH and the moisture barrier is a (1) cellulose material, preferably box board, (2) PVdC layer, or (3) metallized polymeric composite, preferably metallized oriented polypropylene.
• the moisture barrier may be applied to the outer surface of the oxygen barrier.
• the polymeric materials contemplated as the core or substrate of the multilayer structure of the present invention include any polymeric film oriented or unoriented which inherently permits the transmission of oxygen, flavor/odor, and grease/oil wherein the utility of such film would call for a minimization of the transmission of oxygen, flavor/odors, and grease oil.
• the source of the oxygen referred to herein is atmospheric oxygen.
• the source of flavor is the condiment flavor, and the source of odors is from the environment. While nylon, polyethylene terephthalate
• polycarbonate films are contemplated herein, a particularly preferred class of films is the polyolefins.
• polyolefins within the polyolefin class, homopolymers and copolymers of propylene, low density (“LDPE”), and linear low density polyethylene (“LLDPE”) are preferred. High density polyethylene (“HDPE”) may also be used.
• LDPE low density polyethylene
• HDPE High density polyethylene
• the preferred core can be ho opolypropylene having a melting point range of from
• the preferred core layer can also be coextruded with a thin skin layer, amounting to 2 to 12% of the total thickness, of a copolymer of. propylene and another olefin, e.g., ethylene, butene-1.
• the other olefin which can be present in the copolymer is in an amount of from 1 to 7 wt.%.
• the polymeric substrate can be of any desired thickness, although thickness will typically range from 0.5 to 2 mils (0.7 to 3 mils for PVdC coated product) to ensure good machinability on high-speed packaging equipment.
• the OPP film should preferably have a thickness of 1.0 mil (1.75 mils for PVdC coated product).
• a preferred treatment involves treating the surface to a surface tension level of at least 35 and preferably from 38 to 45 dynes/cm in accordance with ASTM Standard D2578-84.
• the treatment can be flame treatment, plasma treatment, chemical treatment or corona discharge treatment. Flame treatment and corona discharge treatment are preferred with corona discharge treatment being particularly preferred.
• a suitable primer material is coated onto the treated surface.
• Preferred primer materials are those disclosed in U.S. Patent No. 4,564,559. These include a primer produced by condensing a onoaldehyde with an interpolymer of acrylamide or methacrylamide and at least one other unsaturated monomer.
• a primer material produced by condensing aminoaldehyde with acrylamide or methacrylamide and subsequently interpolymerizing the condensation product with -at least one other unsaturated monomer in the presence of a C--C 6 alkanol.
• a particularly preferred primer material for the structure contemplated herein has been found to be poly(ethyleneimine) .
• the imine primer provides an overall adhesively active surface for thorough and secure bonding with the subsequently applied cross-linked polyvinyl alcohol and PVdC on the other surface of the substrate when PVdC comprises the moisture barrier.
• an effective coating solution concentration of the poly(ethyleneimine) applied from either aqueous or organic solvent media, such as ethanol is a solution comprising from 0.1 to 0.6% by weight of the poly(ethyleneimine) .
• a commercially available material of this type is known as Polymin P, a product of BASF-Wyandotte Corporation.
• Another particularly preferred primer material is the reaction product of an epoxy resin as a first component with an acidified aminoethylated vinyl polymer as the second component.
• the contemplated epoxy resins are glycidyl ethers of polyhydroxy compounds, such as resorcinol, hydroquinone, Novolac* resins, and the like.
• the specific structure of the epoxy resin is not critical to the primer employed in the present invention, important considerations in the selection of the epoxy resin revolve around its physical state. For example, it must be liquid and capable of being readily dispersed or dissolved with the second component or curing agent as described hereinbelow. If the epoxy resin is of low viscosity, it may be stirred directly into the second component, i.e., curing agent, however, it is preferred to employ the epoxy resin in an aqueous emulsion.
• the second component in the epoxy primer composition of the present invention is an amino modified acrylic polymer which is water soluble.
• This polymer is a curing agent for the epoxy compound.
• the preferred material is described in U.S. Patent No. 3,719,629.
• a liquid epoxy resin is emulsified in a solution of the curing agent by rapid stirring, the resultant dispersion is diluted with water to the desired concentration for coating, usually from 2 to 20% solids.
• the stoichiometric ratio may be varied over a wide range, from 1 epoxy to 3 amine groups through 3 epoxy groups to 1 amine group.
• Any of the above described primers can be employed in the range of 0.001 to 3.5 g/m 2 .
• Polyvinyl alcohol as used in the present invention and claims refers to a normally solid polymeric material, soluble in water, but insoluble in most organic solvents and characterized by the presence of (-CH 2 -CH0H-) units in the polymer chain.
• These polymers are ordinarily prepared by the replacement of the acetate groups of polyvinyl acetate with hydroxyl groups as by hydrolysis or alcoholysis.
• the percent of acetate groups replaced by hydroxyl groups is the degree of hydrolysis PVOH thus formed and indicates the percent of hydroxyl groups present in PVOH out of the total possible hydroxyl groups.
• the crosslinking reaction by which the superior barrier coatings of this invention are obtained proceeds through the hydroxyl groups of PVOH.
• substantially completely hydrolyzed PVOH are useful in this invention.
• substantially completely hydrolyzed in the present specification and claims is meant a degree of hydrolysis of above 85%.
• PVOH having an hydroxyl content above 88% and particularly above 95% provide superior resistance, clarity and flexibility and adhering strength. Hydroxyl group -contents of 99% to 100% provide the best barrier coatings and are particularly preferred for use in this invention.
• the PVOH employed herein can be any commercially available material. For example, ELVANOL 71-30 or ELVANOL 90-50 are E.I. duPont products.
• the PVOH coating solution is prepared by dissolving the polymer in hot water, cooling and mixing both with a suitable crosslinking agent and inorganic acid, preferably sulfuric acid, as the catalyst.
• the crosslinking agent can be a melamine- or urea- formaldehyde resin.
• Commercially available cross-linkers also would include PAREZ 613, a methylated melamine formaldehyde; and CYMEL 373, a methylated melamine formaldehyde; CYMEL 401, a trimethylol melamine urea formaldehyde; glyoxal; and borax.
• Sulfuric acid as the catalyst has been discovered to be far superior to nitric acid, ammonium chloride and ammonium nitrate.
• Crosslinking is carried out to make the PVOH less moisture sensitive but it is essential that this does not substantially occur before the coating weight is applied and evenly distributed. This is effected by making up the aqueous solution so that the initial concentration is too low for this to occur but, as drying occurs, the concentration increases and the rate of crosslinking also increases.
• Suitable concentrations have been found to be from 1 to 35 wt.%, preferably from 4 to 8 wt.% of the solution, which are PVOH plus crosslinking agent plus inorganic acid, e.g. , sulfuric acid, in a catalytically active amount. If the solids content is higher, the solution becomes too viscous; if lower, good water resistance is not obtained. From 5% to 30 wt.%, typically 15% crosslinking agent is used with from 0.1% to 7.5%, typically 2 wt.% of the sulfuric acid catalyst.
• a preferred formulation comprises the following solids content: 85.5 wt.% PVOH;.12.8 wt.% methylated melamine formaldehyde; and 1.7 wt.% sulfuric acid.
• the acid, e.g., sulfuric acid employed can have a strength ranging from 0.1 to 20 wt.%.
• Aqueous PVOH solutions were prepared by dissolving sufficient ELVANOL 71-30 in hot water to form 8 wt.% solution which were then cooled. To these solutions were added a 20 wt.% aqueous melamine formaldehyde solution and the appropriate amount of a solution of aqueous ammonium chloride, sulfuric acid, ammonium sulphate, ammonium nitrate or nitric acid to provide the formulations shown in the Table 1 below.
• Cross-linked PVOH can be present in an amount from 0.2 to 4.5 g/m 2 , usually from 0.4 to 3 g/m 2 .
• the cross-linked PVOH coated films described above are intended, in one embodiment, to be adhered to cellulose materials such as paper, paperboard and fiberboard by adhesion or extrusion lamination.
• the adhesion or extrusion lamination of the cellulose material is to the outer surface of the cross-linked PVOH layer.
• the resulting structure is capable of holding liquids and has a high oxygen and flavor/odor, grease/oil barrier.
• unlaminated box board material has an average oxygen transmission rate ("T0 2 ") in excess of 2300 cc/m 2 /24 hr at 23.8 ⁇ C and 0% relative humidity ("RH”) .
• T0 2 rate was significantly lower, namely 0.309 cc/m 2 /24 hr at 23.8 ⁇ C and 0% RH and 1.55 cc/m 2 /24 hr at 23.8°C and 75% RH.
• the lamination to box board material is accomplished by using an adhesive such as polyurethane, acrylics or PVdC's.
• the resulting structure is then extrusion coated preferably with a sealant layer of SURLYN ® or polyethylene to prevent leaching of any cellulose component into the liquid which comes in contact with the sealant layer and to enhance the moisture barrier of the resulting film structure.
• Containers formed from the packaging film structure of the present invention can be used to package milk, orange juice and wine.
• a cross-linked PVOH film combination laminated to box board an excellent oxygen barrier is provided which requires considerably less coating of cross-linked PVOH than a comparable EVOH film.
• a 48 gauge layer of EVOH film provides an oxygen barrier of 0.62 cc/m 2 /24 hr. at 23.8 ⁇ C, 0% RH and WVTR of 1550 g/m 2 /24 hr at 37.8°C, 90% RH.
• the EVOH has no moisture barrier.
• the same oxygen barrier value and a WVTR value of 5.42 g/m/24 hr at 37.8°C, 90% RH are obtained when a substrate of 79 gauge OPP is covered with only a 3 gauge layer of cross-linked PVOH.
• significant cost savings can be realized as a result of using a much thinner coating of PVOH.
• Cellulose materials useful in the present invention are generally paper products such as paper, paperboard and fiberboard. Although there is no strict distinction between paper and paperboard, paper is considered to be a product made from cellulose fibers which is less than
• Paper used in packaging may be course and fine.
• Course packaging paper is known as kraft paper and is almost always made of unbleached kraft soft wood pulps.
• Fine papers generally made of bleached pulp, are typically used in applications requiring printing, writing, and special functional properties such as barriers to liquid and/or gaseous penetrants.
• Other types of paper useful in the present invention are parchment, grease proof, glassine, water, grease and oil resistant, waxed, specialty-treated, wet-strength papers, all as defined in M. Bakker, The Wiley Encyclopedia of Packaging Technology, 497-500 (1986) .
• a preferred cellulose fiber material useful in the present invention is paperboard.
• Paperboard is a relatively stiff paper product usually greater than 12 mils. The term paperboard is used to distinguish the product from paper which is thin and quite flexible. Paperboard may have single-ply or multi-ply structure. It can be formed on a Fourdrinier wire part, a single or a series of modern formers.
• the single-ply paperboard useful for this invention is made from 100% bleached-chemical wood pulp and can be used for food packaging where purity and clean appearance is required together with a degree of strength and a surface of sufficient quality to accept good-quality print.
• multi-ply paperboard can be used over a much wider range of applications because virgin-pulp outer layers with good appearance, strength, and printing properties can be combined with lower-grade middle plies.
• the general term for this range of paperboard is folding box board.
• paperboard used to produce large and strong cases is also useful in the present invention.
• the materials used for the construction of these containers are made from several layers of paperboard.
• corrugated board two facings are glued to both sides of the corrugating medium to produce a single-wall corrugated board.
• Three facings and two media are used to obtain double-wall corrugated board.
• Triple-wall corrugated board uses four facings and three media.
• single or multi-ply paperboard hard-sized for water resistance according to known techniques in the art is preferred. Types of paperboard and fiberboard are as defined in M.
• the cross-linked PVOH/cellulose material structure of the present invention has excellent oxygen and flavor/odor, grease/oil barrier characteristics and is capable of holding liquids.
• Figure 1 shows a schematic cross-section of a film structure prepared according to the present invention.
• Layer 10 represents a surface treated polymeric substrate which is coated with a primer layer 11 on at least one surface to which a cross-linked PVOH layer 12 is adhered.
• the cross-linked PVOH layer may be printed and then adhered to a cellulose material layer 14 by using an adhesive coating 13.
• the cellulose material may be printed and then adhered to a cross-linked PVOH film structure.
• the resulting structure is extrusion coated with a sealant 15 such as SURLYN ® or polyethylene on the outer surface of the cellulose material.
• the resulting film structure also has enhanced moisture barrier characteristics.
• Figure 2 illustrates another embodiment of the present invention, wherein layer 20 represents a polymeric substrate surface treated on at least one side, primed with a primer coating 21 surface treated and thus adapted to receive a cross-linked PVOH layer 22 which can then be adhered to a cellulose material 24 by using an adhesive coating 23.
• the cellulose material may be printed.
• a sealant 25 such as SURLYN ® or polyethylene on the outer surface of the polymeric substrate to provide an enhanced moisture barrier.
• cross-linked PVOH coated films described above are, in a second embodiment, intended to be adhesively laminated to either oriented or unoriented commercially available thermoplastic films such as homopolymer polypropylene film, polypropylene with coated layers, polypropylene with slip additives, polypropylene with coextruded layers, opaque polypropylene, polyethylene, nylon, polyethylene terephthaiate, polycarbonate, polystyrene, etc.
• a preferred class of films are the polyolefins. Most preferred is a polymeric substrate of OPP having a thickness of 1.50 mil.
• the cross-linked PVOH coated films described above may be coated with other coatings to enhance other desirable properties, such as moisture barrier properties.
• PVdC is a particularly preferred coating that could be applied to the above cross-linked PVOH film combination.
• the resulting film has excellent oxygen, flavor/odor, grease/oil and moisture barrier properties. Additionally, the film is also heat sealable, and quite sturdy.
• the PVdC coated film of the present invention can be used as a mono web providing the user with significant cost savings.
• PVdC also more correctly referred to as copolymers of vinylidene chloride
• PVdC copolymers of vinylidene chloride
• VdC copolymers are copolymers of 65 to 96% by weight of vinylidene chloride and 4 to 35% of one or more comonomers such as vinyl chloride, acrylonitrile, methacrylonitrile, methyl methacrylate, or methyl acrylate, hereafter referred to as PVdC.
• a suitable grade contains 7 weight percent methacrylonitrile, 3 weight percent methyl methacrylate, and 0.3 weight percent itaconinic acid comonomers.
• PVdC customarily include formulation additives such as waxes, fatty acids and derivatives thereof, particulate matter, and polymeric species such as mixed polyesters. Such additives may be useful to reduce brittleness and stiffness of the polymer or to improve its heat sealability and handling properties.
• Commercially available VdC copolymers useful for the present invention are manufactured by Morton Co.
• an uncoated film had an oxygen transmission rate ("T0 2 ”) in excess of 2324.9 cc/m 2 /24 hr. at 23.8 ⁇ C, 0% relative humidity (“RH”)/and a water vapor transmission rate ("WVTR") of 5.58 g/m/24 hr at 37.8°C. 90% RH.
• a film combination according to this embodiment of the present invention coated with both cross-linked PVOH and PVdC had a T0 2 of 0.31 cc/m 2 /24hr at 23.8°C 75% pH.
• the WVTR was 2.325 g/m 2 /24 hr at 37.8 ⁇ C.
• Fig. 3 shows a schematic cross section of a film prepared by the present invention.
• Layer 30 represents the treated polymeric core which is coated with a poly(e hyleneimine) layer 31 on one surface and dry epoxy primer 32 on the other surface.
• the cross-linked PVOH layer 33 is adhered to the surface bearing poly(ethyleneimine) primer and the PVdC layer 34 is adhered to the other epoxy coated surface.
• the PVOH/PVdC film structure described above is used as a mono web and thus provides more cost effective packaging than other films which require more than one web.
• a mono web is a term adapted by plastic resin processors to denote a single plastic film, not as a final discrete article but as a long film somewhere in the processing stage, frequently being drawn off a large roll of printed film.
• PVdC the sealant layer coming in contact with the food product
• the cross-linked PVOH layer can also be printed.
• a white film may be applied to the cross-linked PVOH or the PVdC layer.
• Commercially available opaque polypropylene from Mobil Chemical, Films Division is a preferred white film.
• the cross-linked PVOH layer may be laminated to another film that provides improved strength and barrier.
• films include, PET, nylon and polyolefins.
• either surface may be further laminated with a layer of polyethylene.
• PVOH/PVdC film structures of the present invention are transparent so that packaged condiments and sauces can be freely inspected and scanned for contaminants.
• the cross-linked PVOH coated films described above are intended, in a third embodiment, to be adhesively laminated to either oriented or unoriented commercially available thermoplastic films such as homopolymer polypropylene film, polypropylene with coated layers, polypropylene with slip additives, polypropylene with coextruded layers, opaque polypropylene, polyethylene, nylon, polyethylene terephthaiate, polycarbonate, polystyrene, etc.
• a preferred class of films are the polyolefins. Most preferred is a polymeric substrate of OPP having a thickness of 1.00 mil.
• moisture barrier materials such as metallized films, preferably metallized OPP.
• the metallized films useful in the present invention provide excellent moisture barrier, but inherently permit the transmission of oxygen. By laminating a cross-linked PVOH film combination to metallized film, a multi-layer film structure is obtained which has significantly enhanced oxygen and moisture barrier.
• metallized oriented polypropylene is most preferred.
• Commercially available metallized OPP is available from Mobil . Chemical, Films Division (Bicor 70MB-HB) .
• Many commercially available metallized OPP films are composites consisting of a polypropylene core having, on at least one of its surfaces, a relatively thin layer of a propylene-ethylene copolymer. The copolymer layer is subjected to a corona discharge treatment and the coating metal is then deposited by such methods as electroplating, sputtering, or vacuum metallizing.
• the metal may be aluminum, copper, silver, or chromium.
• a preferred metallized OPP and method of manufacture is disclosed in U.S. Patent No. 4,345,005.
• Commercially available metallized OPP has excellent moisture barrier properties as shown by a very low water vapor transmission rate ("WVTR"), typically 0.775 g/m 2 / 24 hr at 37.8 ⁇ C, 90% relative humidity (“RH”) .
• WVTR water vapor transmission rate
• RH 90% relative humidity
• T0 2 average oxygen transmission rate
• T0 2 average oxygen transmission rate
• the combination of metallized OPP with cross-linked PVOH coated film creates a structure that provides both, excellent moisture and oxygen barrier.
• Metallized films known in the art can be laminated to the cross-linked PVOH film combinations by applying an adhesive coating onto the cross-linked PVOH layer.
• the adhesive bonds the metallized film onto the PVOH bearing surface of the polymeric substrate.
• the cross- linked PVOH layer Prior to applying the adhesive, can be ink printed.
• the adhesive can be any adhesive used with metallized films, polyurethane being preferred.
• the metallized film can also be attached to the cross-linked PVOH film combination by polymounting, i.e., extrusion lamination. Extrusion lamination is a known process for joining two webs by feeding them through a machine that extrudes a thin layer of plastic between them to act as an adhesive.
• FIG. 4 illustrates this latter embodiment of the present invention.
• Layer 40 represents a surface treated polymeric substrate which is coated with a primer layer 41 on at least one surface thereof.
• a cross-linked PVOH layer 42 is adhered to the surface treated substrate.
• the cross-linked PVOH film combination is adhesively laminated to a metallized film layer 44 by applying an adhesive coating 43 onto the cross-linked PVOH bearing surface.
• EXAMPLE 1 A homopolymer polypropylene core layer was coextruded with skin layers of an ethylene-propylene random copolymer.
• the random copolymer contained 3 to 5% by weight of ethylene.
• the extruded film was biaxially oriented to 4 to 5 times machine direction and 7 to 10 times transverse direction to yield a film having a thickness of 1 mil.
• the thickness of the skin layers was 8% of the film and they were of equal thickness.
• This film combination was corona discharge treated in accordance with commonly employed prior art techniques to produce a surface with a wetting tension of 42 dynes/cm.
• the treated film was precoated on both sides with 0.1 wt.% poly(ethyleneimine) , as manufactured by BASF-
• the dried film was then tested in an oxygen- permeability device in which a stream of dry oxygen was passed through an aqueous salt solution-permeated pad to control the gas moisture content and then through the film, disposed at right angles to the stream with the cross-linked PVOH coating upstream.
• the oxygen transmitted was determined and the amount of oxygen passed per unit area of film per time period was calculated.
• Samples bearing cross-linked PVOH layer obtained by using sulfuric acid catalyzed systems were superior to any other catalyzed system for inhibiting the transmission of oxygen through a packaging film.
• the rubbing resistance of the sulfuric acid catalyzed film combinations was also outstanding. Oxygen transmission and rubbing resistance rates for several samples bearing PVOH cross-linked in the presence of methylated melamine formaldehyde, ammonium chloride and sulfuric acid are set forth in Table 1 below.
• Table 1 illustrates that samples bearing PVOH cross- linked with sulfuric acid have oxygen transmission rate and rubbing resistance values far superior to those cross-linked with ammonium chloride.
• a cross-linked PVOH coating was applied to a 1.00 mil OPP film, surface treated and primed as in Example 1 above.
• the resulting film combination was laminated on the cross-linked PVOH bearing surface with a box board by using a polyurethane adhesive coated onto the box board.
• Thickness is measured in mil.
• EXAMPLE 3 A homopolymer polypropylene core layer was coextruded with skin layers of an ethylene-propylene random copolymer.
• the random copolymer contained 3 to 5% by weight of ethylene.
• the extruded film was biaxially oriented to 4 to 5 times machine direction and 7 to 10 times transverse direction to yield a film having a thickness of 1 mil.
• the thickness of the skin layers was 8% of the film and they were of equal thickness.
• This film combination was corona discharge treated in accordance with commonly employed prior art techniques to produce a surface with a wetting tension of 42 dynes/cm.
• the treated film was precoated on one side with 0.1 wt% poly(ethyleneimine) , as manufactured by BASF-Wyandotte Corporation Polyamin P product and on the other with epoxy of 0.075g/m 2 .
• the film was air-dried at 100°C. This coating weight was too low to be measured, but was calculated to be in the range of 0.002g/m 2 by optical density.
• the primer coated treated substrate was then coated on one surface with a PVdC coating weight of 4.5 g/m 2 .
• the PVdC coating was a 50 wt % aqueous latex solution resulting from the polymerization of VdC with methyl acrylic acid.
• the opposite surface of this film structure was then coated with the appropriate solution of PVOH, cross-linking agent and catalyst.
• the solutions were applied utilizing a reverse direct gravure coater and the coated film was passed through a dry-air oven at from 100 to 125 ⁇ C. This produced a coating weight of 0.5 g/m 2 .
• the thickness of the polymeric film structure of the present example including both PVOH and PVdC was 1.7 mil.
• the dried films were then tested in an oxygen- permeability device in which a stream of dry oxygen was passed through an aqueous salt solution-permeated pad to control the gas moisture content and then through the film, disposed at right angles to the stream with the cross-linked PVOH coating upstream.
• the oxygen transmitted was determined and the amount of oxygen passed per unit area of film per time period was calculated.
• Samples bearing cross-linked PVOH layer obtained by using sulfuric acid catalyzed systems were superior to any other catalyzed system for inhibiting the transmission of oxygen through packaging films.
• the rubbing resistance of the sulfuric acid catalyzed film combinations was also outstanding.
• Oxygen transmission and rubbing resistance rates for several samples bearing PVOH cross-linked in the presence of methylated melamine formaldehyde, ammonium chloride and sulfuric acid are set forth in Table 3 below.
• Table 3 illustrates that samples bearing PVOH cross- linked with sulfuric acid have oxygen transmission rate and rubbing resistance values far superior to those cross-linked with ammonium chloride. After testing for oxygen permeability was completed, the films were tested for moisture barrier by measuring the water vapor transmission rate ("WVTR”) .
• WVTR water vapor transmission rate
• T0 2 and WVTR values for an uncoated OPP film, an OPP film coated only with cross-linked PVOH and an OPP film coated with both cross-linked PVOH and PVdC are set forth in Table 4 below.
• the WVTR was measured as described in ASTM F372.
• an uncoated OPP film shows a high oxygen transmission rate as a result of poor oxygen barrier properties.
• the oxygen transmission rate is significantly decreased by the addition of a layer of cross-linked PVOH.
• both the oxygen barrier and the moisture barrier properties of the resulting film structure are considerably enhanced.
• the oxygen barrier properties of the PVdC are largely insensitive to moisture, i.e., relative humidity independent. Therefore, even under very extreme conditions, where the barrier properties of the PVOH have been degraded, the PVdC maintains the oxygen transmission rate at less than 15.34 cc/m 2 /24 hr.
• the use of two oxygen barrier layers minimizes the chances of two pin holes from occurring in the lining up of the coating. This reduces the oxygen transmission rate by an amount greater than ordinarily expected.
• EXAMPLE 4 A homopolymer polypropylene core layer was coextruded with skin layers of an ethylene-propylene random copolymer.
• the random copolymer contained 3 to 5% by weight of ethylene.
• the extruded film was biaxially oriented to 4 to 5 times machine direction and 7 to 10 times transverse direction to yield a film having a thickness of 1 mil.
• the thickness of the skin layers was 12% of the film and they were of equal thickness.
• This film combination was corona discharge treated in accordance with commonly employed prior art techniques to produce a surface with a wetting tension of 42 dynes/cm.
• the treated film was precoated on both sides with 0.1 wt% poly(ethyleneimine) , as manufactured by BASF-Wyandotte Corporation Polyamine P product.
• the film was air-dried at 100°C. This coating weight was too low to be measured, but was calculated to be in the range of 0.002 g/m 2 .
• One treated and primed surface of this film structure was then coated with the appropriate solution of PVOH, cross-linking agent and catalyst. The solutions were applied utilizing a reverse direct gravure coater and the coated film was passed through a dry-air oven at from 100 to 125"C. This produced a coating weight of 0.5 g/m 2 .
• the dried films were then tested in an oxygen- permeability device in which a stream of dry oxygen is passed through an aqueous salt solution-permeated pad to control the gas moisture content and then through the films, disposed at right angles to the stream with the cross-linked PVOH coating upstream.
• the oxygen transmitted was determined and the amount of oxygen passed per unit area of film per time period was calculated.
• Samples bearing cross-linked PVOH layer obtained by using sulfuric acid catalyzed systems were superior to any other catalyzed system for inhibiting the transmission of oxygen through the packaging films.
• the rubbing resistance of the sulfuric acid catalyzed film combinations was also outstanding.
• Oxygen transmission and rubbing resistance rates for several samples bearing PVOH cross-linked in the presence of methylated melamine formaldehyde, ammonium chloride and sulfuric acid are set forth in Table 5 below.
• Table 5 illustrates that samples bearing PVOH cross- linked with sulfuric acid have oxygen transmission rate and rubbing resistance values far superior to those cross-linked with ammonium chloride.
• a cross-linked PVOH coating was applied to a 1.00 mil OPP film, surface treated and primed as in Example 4 above.
• the resulting film combination was laminated onto the cross-linked PVOH bearing surface with a layer of metallized OPP.
• the lamination was carried out by using a coating of polyurethane adhesive over the vacuum deposited aluminum surface of the metallized OPP.
• the resulting structure had excellent oxygen and moisture barrier properties as illustrated in Table 6 below.
• the thickness is measured in mil.
• Table 6 further illustrates that a typical metallized OPP provides an excellent moisture barrier; however, with T0 2 values from 30 to 77 cc/m 2 /24 hr the oxygen barrier properties of metallized OPP are inadequate for many applications. Consequently, when a metallized OPP layer is laminated or polymounted onto a film combination including cross-linked PVOH, the resulting structure has both excellent oxygen and moisture barrier properties.

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• 1995
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